TONY JONES, PRESENTER: The American soldier convicted of the biggest intelligence breach in US history for providing classified files to WikiLeaks has been sentenced to 35 years jail. Last month, Army Private Bradley Manning was found guilty of 20 offences, including espionage. Tonight, in a remarkable twist, Manning's lawyer says he expects his client will be pardoned and Manning himself has issued a statement saying he wants to live as a woman named Chelsea. North America correspondent Jane Cowan reports.

JANE COWAN, REPORTER: It's a case that commanded international attention, and as Bradley Manning heads to a military prison, supporters made their displeasure known outside the White House.

Hours earlier, Private Manning arrived at court in Maryland one last time, delivering a sentence less than the 60 years prosecutors wanted, but more than the 25 years the defence sought. The military judge, Colonel Denise Lind, ordered Private Manning to spend 35 years in a military jail. The former Army intelligence analyst showed no emotion, even as supporters called out and his sister wept.

DAVID COOMBS, MANNING DEFENCE LAWYER: Myself and others were in tears and he looks to me and says, "It's OK. It's alright. Don't worry about it. It's alright. I know you did your best."

JANE COWAN: The 25-year-old who leaked hundreds of thousands of sensitive diplomatic cables and battlefield reports could be a 60-year-old man before he's free, although he'll be eligible for parole in seven years. He made a final statement through his lawyer.

DAVID COOMBS: (Reading from Manning's statement) "I will serve my time knowing that sometimes you have to pay a heavy price to live in a free society."

JANE COWAN: It's perhaps an indication of how the American public sees the case that this is how many people turned out to protest Bradley Manning's sentence. His lawyer though is vowing to fight on, asking the US President Barack Obama to pardon Private Manning and release him immediately.

Private Manning's leaks exposed the abuse of detainees by Iraqi officers under the watch of American forces and showed the civilian death toll of the Iraq War was most likely significantly higher than official estimates. Amongst the more shocking material he revealed was the cockpit video of a US Apache helicopter crew firing on suspected insurgents in Baghdad, but killing a Reuters news photographer and his driver.

The sentence is the harshest given to anyone for leaking US Government information to the media.

LISA WINDSOR, FORMER LAWYER, JUDGE ADVOCATE GENERAL: There is nothing glorified in what he did. Releasing classified information just wantonly, the way he did, could have had a horrendous adverse effect on national security and could have cost service members' lives and he really didn't consider that.

JULIAN ASSANGE, WIKILEAKS FOUNDER: The minimum sentence to be applied is as little as 5.2 years once you include time off for good behaviour, parole dates, compensation for the - his torturous treatment in prison. So this is a really important tactical victory for his defence team, his campaign team and his support community.

JANE COWAN: One man familiar with the US system of military justice is the former Marine Corps lawyer Dan Mori, who represented Australian Guantanamo Bay detainee David Hicks. He says the real question remains whether Bradley Manning is just a bit player in the US Government's quest to go after the bigger fish in the equation, Julian Assange.

DAN MORI, FORMER US MILITARY LAWYER: The question is does this 35-year sentence give a bigger hammer to the US Government to try to make Manning cooperate and assist with the Government, if that's even being sought?

JANE COWAN: Critics of the Manning case say it sets a dangerous precedent for whistleblowing and for others who might be in the wings of the US justice system like the NSA contractor Edward Snowden. Private Manning's lawyer, David Coombs, says the hefty sentence raises difficult questions for America as a country.

DAVID COOMBS: The case of the United States v Bradley Manning is a watershed moment in history for freedom of the press. We need to decide what freedoms and individual rights we are willing to give up in the name of national security.

JANE COWAN: The Manning case qualifies for an automatic appeal, which is likely to start late next year.